[TASK] Configure the target PHP version for PHPStan

[oliverklee]

This will help avoid it suggesting things that are only possile in later PHP versions.

Fixes #1214

[coveralls]

coverage: 52.048%. remained the same
when pulling 52deb82 on task/configure-phpstan-php-version
into 734c72e on main.

[JakeQZ]

This isn't working as well as it should. With PHP 8.3 on the server, it's picking up that int<0, max> and int<1, max> are not compatible:

  Line   src/Position/Position.php (in context of class                               
         Sabberworm\CSS\Tests\Unit\Position\Fixtures\ConcretePosition)                
 ------ ----------------------------------------------------------------------------- 
  62     Parameter #1 $lineNumber (int<1, max>|null) of method                        
         Sabberworm\CSS\Tests\Unit\Position\Fixtures\ConcretePosition::setPosition()  
         should be contravariant with parameter $lineNumber (int<0, max>|null)        
         of method Sabberworm\CSS\Position\Positionable::setPosition()                
         🪪  method.childParameterType                                                

But with PHP 7.4 on Windows, this error is not found. In both cases, PHPStan version is 2.1.2. Context is #1221 (where I will now correct the Positionable::setPosition DocBlock to int<1, max>|null for $lineNumber).

Oddly, this doesn't invlove a native declaration, but a DocBlock annotation, which should be independent of PHP version (target or runtime).

Also, the error Parameters should have "Sabberworm\\CSS\\CSSList\\CSSListItem\|array" types as the only types passed to this method has not gone away with this change. Native union types require PHP 8.0.

This change involved no changes to the baseline. Whereas the equivalent change to Emogrifier did.

I wonder if PHPStan is even picking up the setting at all. A difference between the config files is that the parameters section of the one here begins with a parallel setting, whereas the one in Emogrifier begins with the phpVersion setting.

[JakeQZ]

This isn't working as well as it should. With PHP 8.3 on the server, it's picking up that int<0, max> and int<1, max> are not compatible:

Scrub that. Just ran it again with PHP 7.4, and it picked up the error. Maybe I didn't run the full set of tests before finally committing (I was playing around with nullability to check that if I'd got it wrong it would be picked up).

Also, the error Parameters should have "Sabberworm\\CSS\\CSSList\\CSSListItem\|array" types as the only types passed to this method has not gone away with this change. Native union types require PHP 8.0.

This change involved no changes to the baseline. Whereas the equivalent change to Emogrifier did.

I wonder if PHPStan is even picking up the setting at all. A difference between the config files is that the parameters section of the one here begins with a parallel setting, whereas the one in Emogrifier begins with the phpVersion setting.

This is still a bit of a mystery, however.